The invention relates to a semiconductor diode laser array comprising a semiconductor layer structure having a number of substantially parallel strip-shaped active regions each located between two enclosure layers having a larger band gap and a smaller refractive index for the radiation produced than the active region, which active regions are disposed within a resonant cavity and constitute at least two groups located in two substantially equidistant planes, at least one of the groups comprising at least two active regions.
Such semiconductor diode layer arrays are suitable radiation sources for inter alia data processing systems, such as laser printers, by means of which information is written, and such as "optical disk" systems, in which information is read out--for example so-called compact disk (CD) and Video Long Play (VLP) players--or written and read out--for example digital optical recording (DOR).
A semiconductor diode laser array of the kind described above is known from British Patent Application published under No. GB 2164206 A. In this document, a semiconductor diode laser array is described, in which an active layer is provided between two enclosure layers on a substrate provided with mesa-shaped strips between which channels are disposed. The strip-shaped active regions of the semiconductor diode lasers are disposed alternately on the upper side of the mesa-shaped strip and on the bottom of the channel located between two of these strips. Both the active layer and the two enclosure layers of each semiconductor laser extend continuously over the edges of the mesa-shaped strip and thus connect the active region of each laser to the active region of adjacent layers, although these layers are slightly thinner at the edges than elsewhere. By means of the slightly thicker part of the active layer at the edges, the radiation produced in an active region of a semiconductor diode laser is coupled in phase to the radiation produced in the active regions of the adjacent semiconductor diode lasers.
A disadvantage of the known device is that both due to the leakage of radiation from the active region of a semiconductor diode laser to the active layer between two semiconductor diode lasers and due to parasitic emission in the last-mentioned part of the active layer the starting current of the device is fairly high.
A further disadvantage of this known laser array resides in the fact that the positioning of the semiconductor diode lasers located on top of the mesas with respect to the semiconductor diode lasers located on the bottom of the channels is fixed within certain limits determined by the geometry; thus, for example, it is not possible to arrange four semiconductor diode lasers pairwise accurately one above the other so that a 2+2 symmetrical matrix is obtained. For the given 2+2 array, this can mean that a non-optimal symmetrical far field is obtained.